1. Field of the Invention
The invention generally relates to the drivetrain for an off highway agricultural vehicle. More specifically, the invention relates to an axle having a differential positioned between two axle half-shafts, and incorporates a dual planetary gear set between and interconnecting each axle half-shaft to the differential.
2. Related Technology
In general, off highway and agricultural vehicle power levels are increasing at an exponential rate. Axles are traditionally the drive train component most sensitive to the increase in power because of the high gear reductions and increased vertical loads that are synonymous with higher power. Axles generally provide in the range of 25:1 to 50:1 reductions in input speed, creating high torque levels in the rotating components, and having a negative impact on axle life and reliability. Traditionally, agricultural axles include a three pinion, single inboard planetary gear set.
The most common solution for handling additional power has been to increase the size of the components. However, on large machines, the component sizes have grown outside of the conventional manufacturing limits, thereby making such components very expensive to manufacture. Additionally, many vehicles must remain compact due to performance and/or space limitations. Axles having such large sized components often to do not fit within the desired vehicle design.
Conventional axles typically have two large input speed reductions. First, there is approximately a 6:1 reduction in the differential. Then, a planetary gear set, positioned between the differential and the axle half-shaft, provides a second reduction of approximately 6:1. This achieves an over-all reduction of approximately 36:1. The torque levels associated with the 6:1 reduction within the differential and within the planetary gear set require larger, heavier components as mentioned before. The larger the relative reduction, the larger the torque loads will be.
Therefore, there is a need for an axle assembly that will accommodate the higher loads associated with increased power output of modern agricultural vehicle, while being compact enough to fit within limited packaging constraints.